Uniform Lithium Deposition Induced by Polyacrylonitrile Submicron Fiber Array for Stable Lithium Metal Anode

The shield-like nano-sized Si3N4 derivatives to defend against the attack of lithium dendrites

The unrestrained Li dendrite growth impedes the performance of Li metal batteries (LMBs) and brings safety concerns. To mitigate the unfavorable effect of Li dendrites, in this work, a shield-like artificial interlayer composed of Si3N4 is employed to achieve the desirable electrochemical performance of LMBs. The Si3N4-based interlayer can in-situ electrochemically react with Li to generate inorganic Li3N and LixSi alloys: the former with high ionic conductivity can effectively enhance the Li+ transference, while the latter with reversibility for Li+ insertion/deinsertion can act as Li+ reservoir to modulate Li+ platting/stripping. Thus, the Si3N4-derived compound shield effectively defends against the attack of Li dendrites and suppresses their growth, with which the Li||Li cells can cycle at 1 mA cm-2 (1 mAh cm-2) up to 500 h and the LiFePO4 (LFP) ||Li batteries can operate 400 cycles at 1C with 91.5 % capacity retention.

A Strategy for Preparing Solid Polymer Electrolytes Containing In Situ Synthesized ZnO Nanoparticles with Excellent Electrochemical Performance

ZnO nanoparticles were successfully in situ synthesized in the form of PEO–COO⁻ modified ZnO by a three-step method, based on which the solid polymer electrolytes (SPEs), based on polyethylene oxide (PEO) with excellent electrochemical performance, were prepared. The evolution of the electrochemical and mechanical performances of the SPEs with the ZnO content (0–5 wt.%) was investigated in detail. The mechanical property of the SPEs demonstrated a Λ-shaped change trend as increasing the ZnO content, so that the highest value was acquired at 3 wt.% ZnO. The SPE containing 3 wt.% ZnO had the most outstanding electrochemical performance, which was significantly better than that containing directly-added ZnO (2 wt.%). Compared with the latter, the ion conductivity of the former was improved by approximately 299.05% (1.255 × 10⁻³ S·cm⁻¹ at 60 °C). The lithium-ion migration number was improved from 0.768 to 0.858. The electrochemical window was enhanced from 5.25 V to 5.50 V. When the coin cell was subject to the cycling (three cycles in turn from 0.1 C to 3 C, and subsequent fifty cycles at 1 C), the 68.73% specific capacity was retained (106.8 mAh·g⁻¹). This investigation provides a feasible approach to prepare the SPEs with excellent service performance.

Remedies to Avoid Failure Mechanisms of Lithium-Metal Anode in Li-Ion Batteries

Rechargeable lithium-metal batteries (LMBs), which have high power and energy density, are very attractive to solve the intermittence problem of the energy supplied either by wind mills or solar plants or to power electric vehicles. However, two failure modes limit the commercial use of LMBs, i.e., dendrite growth at the surface of Li metal and side reactions with the electrolyte. Substantial research is being accomplished to mitigate these drawbacks. This article reviews the different strategies for fabricating safe LMBs, aiming to outperform lithium-ion batteries (LIBs). They include modification of the electrolyte (salt and solvents) to obtain a highly conductive solid–electrolyte interphase (SEI) layer, protection of the Li anode by in situ and ex situ coatings, use of three-dimensional porous skeletons, and anchoring Li on 3D current collectors.

Constructing nitrided interfaces for stabilizing Li metal electrodes in liquid electrolytes

Traditional Li ion batteries based on intercalation-type anodes have been approaching their theoretical limitations in energy density. Replacing the traditional anode with metallic Li has been regarded as the ultimate strategy to develop next-generation high-energy-density Li batteries. Unfortunately, the practical application of Li metal batteries has been hindered by Li dendrite growth, unstable Li/electrolyte interfaces, and Li pulverization during battery cycling. Interfacial modification can effectively solve these challenges and nitrided interfaces stand out among other functional layers because of their impressive effects on regulating Li⁺ flux distribution, facilitating Li⁺ diffusion through the solid-electrolyte interphase, and passivating the active surface of Li metal electrodes. Although various designs for nitrided interfaces have been put forward in the last few years, there is no paper that specialized in reviewing these advances and discussing prospects. In consideration of this, we make a systematic summary and give our comments based on our understanding. In addition, a comprehensive perspective on the future development of nitrided interfaces and rational Li/electrolyte interface design for Li metal electrodes is included.

In this perspective, we make a systematic summary and give out our comments on constructing nitrided interfaces for stabilizing Li metal electrodes.

Comparative performance of ex situ artificial solid electrolyte interphases for Li metal batteries with liquid electrolytes

The design of artificial solid electrolyte interphases (ASEIs) that overcome the traditional instability of Li metal anodes can accelerate the deployment of high-energy Li metal batteries (LMBs). By building the ASEI ex situ, its structure and composition is finely tuned to obtain a coating layer that regulates Li electrodeposition, while containing morphology and volumetric changes at the electrode. This review analyzes the structure-performance relationship of several organic, inorganic, and hybrid materials used as ASEIs in academic and industrial research. The electrochemical performance of ASEI-coated electrodes in symmetric and full cells was compared to identify the ASEI and cell designs that enabled to approach practical targets for high-energy LMBs. The comparative performance and the examined relation between ASEI thickness and cell-level specific energy emphasize the necessity of employing testing conditions aligned with practical battery systems.

Free-standing lithiophilic Ag-nanoparticle-decorated 3D porous carbon nanotube films for enhanced lithium storage

Lithium metal batteries are promising candidates for next generation high energy batteries. However, an undesirable dendrite growth hinders their practical applications. Herein, a three-dimensional (3D) porous carbon nanotube film decorated with Ag nanoparticles (CNT/Ag) has been synthesized via the thermal decomposition reaction of AgNO₃ into Ag nanoparticles, and then is transformed into a 3D porous CNT/Ag/Li film via thermal infusion to obtain a high-performance free-standing lithium host. This as-formed 3D CNT/Ag/Li host can effectively restrain the dendrite growth by guiding Li deposition via the highly lithiophilic Ag nanoparticle seeds and lowering local current density of the highly conductive matrix. The as-prepared CNT/Ag/Li electrode exhibits long-term cycling stability over 200 cycles at a current density of 1 mA cm⁻² with an areal capacity of 1.0 mA h cm⁻². Moreover, the full cell paired with a sulfur/C cathode shows good cycling stability. Therefore, the 3D porous CNT/Ag/Li film formed via a facile three-step fabrication process can enlarge the cycle lifetime of a lithium metal anode.

A 3D porous CNT/Ag/Li film as a high-performance free-standing lithium host has been synthesized via combining a thermal decomposition process and thermal infusion process.

Polymer Electrolyte Film as Robust and Deformable Artificial Protective Layer for High-Performance Lithium Metal Anode

Lithium (Li) metal anode is a promising candidate for next-generation high capacity energy storage systems. Unfortunately, the uneven deposition/dissolution of Li metal hinders its wide applications. Herein, a robust and deformable polymer electrolyte film as the advanced protective layer on Li metal is developed by a simple tape-casting method, in which the polymer endows a comfortable interfacial contact as well as membrane flexibility to adapt the volume change, while the coordination between the polymer and Li salt provides fast Li⁺ ion diffusion channels. The modified Li metal anodes deliver a stable cycling over 1000 cycles under a high current density of 3 mA cm^-2 in the ether-based electrolyte. The enhanced cycling performance at high current densities are mainly attributed to the Li plating occurred beneath the ion-conducting protective layer, which facilitates Li⁺ ion uniform distribution and further suppresses Li dendrite growth. Accordingly, constructing a polymer electrolyte protective film onto the Li metal anodes is a facile and low-cost methodology to drive the Li metal anode toward practical application.

Inducing the Formation of In Situ Li3N-Rich SEI via Nanocomposite Plating of Mg3N2 with Lithium Enables High-Performance 3D Lithium-Metal Batteries

Lithium metals fit the growing demand of high-energy density rechargeable batteries because of their high specific capacity and low redox potential. However, the lithium-metal anodes are abandoned because of various defects. In this study, we apply composite plating into the protection of lithium-metal anodes. We confirmed that the Mg₃N₂ nanoparticle dispersed in the ether electrolyte can be easily composite-plated with lithium, resulting in a flat, dense, and dendrite-free lithium deposition layer during the electrodeposition process. In addition, the Mg₃N₂ plated in the lithium metal phase would react with lithium and then generate a Li₃N-rich solid electrolyte interphase (SEI) layer, mitigating continuous side reactions of the electrolyte on the Li metal. In addition, another product of the reaction is Mg which can work as lithiophilic sites in electrodeposition. The combined effect of the two fields can effectively improve the performance of lithium metal anodes. The Li₃N-rich SEI layer would grow well on the surface of the three-dimensional (3D) lithium anode by composite plating. Furthermore, composite plating with the Mg₃N₂-containing electrolyte is a viable route that can be used for various 3D current collectors easily with a small volume effect. Here, we show that the composite plating 3D lithium metal anode is successfully applied in the Li-S battery with a long lifetime.

Uniform Li deposition regulated via three-dimensional polyvinyl alcohol nanofiber networks for effective Li metal anodes

Lithium metal anodes are considered to be the most promising anode material for next-generation advanced energy storage devices due to their high reversible capacity and extremely low anode potential. Nevertheless, the formation of dendritic Li, induced by the repeated breaking and repairing of solid electrolyte interphase layers, always causes poor cycling performance and low coulombic efficiency, as well as serious safety problems, which have hindered the practical application of Li anodes for a long time. Herein, we design an electrode by covering a polyvinyl alcohol layer with a three-dimensional nanofiber network structure through an electrospinning technique. The polar functional groups on the surface of the polymer nanofibers can restrict the deposition of Li along the fibers and regulate the deposition of Li uniformly in the voids between the nanofibers. Owing to the structural features of the polymer, the modified Li|Cu electrode displays excellent cycle stability, with a high coulombic efficiency of 98.6% after 200 cycles at a current density of 1 mA cm-2 under a deposition capacity of 1 mA h cm-2, whilst the symmetric cell using the polymer modified Li anode shows stable cycling with a low hysteresis voltage of ∼80 mV over 600 h at a current density of 5 mA cm-2.

Developing High-Performance Lithium Metal Anode in Liquid Electrolytes: Challenges and Progress

Lithium metal anodes are potentially key for next-generation energy-dense batteries because of the extremely high capacity and the ultralow redox potential. However, notorious safety concerns of Li metal in liquid electrolytes have significantly retarded its commercialization: on one hand, lithium metal morphological instabilities (LMI) can cause cell shorting and even explosion; on the other hand, breaking of the grown Li arms induces the so-called "dead Li"; furthermore, the continuous consumption of the liquid electrolyte and cycleable lithium also shortens cell life. The research community has been seeking new strategies to protect Li metal anodes and significant progress has been made in the last decade. Here, an overview of the fundamental understandings of solid electrolyte interphase (SEI) formation, conceptual models, and advanced real-time characterizations of LMI are presented. Instructed by the conceptual models, strategies including increasing the donatable fluorine concentration (DFC) in liquid to enrich LiF component in SEI, increasing salt concentration (ionic strength) and sacrificial electrolyte additives, building artificial SEI to boost self-healing of natural SEI, and 3D electrode frameworks to reduce current density and delay Sand's extinction are summarized. Practical challenges in competing with graphite and silicon anodes are outlined.

3D Fiber-Network-Reinforced Bicontinuous Composite Solid Electrolyte for Dendrite-free Lithium Metal Batteries

Replacement of flammable organic liquid electrolytes with solid Li⁺ conductors is a promising approach to realize excellent performance of Li metal batteries. However, ceramic electrolytes are either easily reduced by Li metal or penetrated by Li dendrites through their grain boundaries, and polymer electrolytes are also faced with instability on the electrode/electrolyte interface and weak mechanical property. Here, we report a three-dimensional fiber-network-reinforced bicontinuous solid composite electrolyte with flexible Li⁺-conductive network (lithium aluminum titanium phosphate (LATP)/polyacrylonitrile), which helps to enhance electrochemical stability on the electrode/electrolyte interface by isolating Li and LATP and suppress Li dendrites growth by mechanical reinforcement of fiber network for the composite solid electrolyte. The composite electrolyte shows an excellent electrochemical stability after 15 days of contact with Li metal and has an enlarged tensile strength (10.72 MPa) compared to the pure poly(ethylene oxide)-bistrifluoromethanesulfonimide lithium salt electrolyte, leading to a long-term stability and safety of the Li symmetric battery with a current density of 0.3 mA cm^-2 for 400 h. In addition, the composite electrolyte also shows good electrochemical and thermal stability. These results provide such fiber-reinforced membranes that present stable electrode/electrolyte interface and suppress lithium dendrite growth for high-safety all-solid-state Li metal batteries.

VGCF 3D conducting host coating on glass fiber filters for lithium metal anodes

VGCF 3D conducting host coating on a glass fiber filter has been demonstrated for its use as a lithium metal anode.

A review of flexible lithium–sulfur and analogous alkali metal–chalcogen rechargeable batteries

This review summarizes recent progress in flexible Li–S and analogous alkali metal–chalcogen batteries, including flexible chalcogen cathodes, flexible alkali metal anodes, flexible solid-state electrolytes, and flexible battery prototypes.